1. Field of the Invention
The present invention relates to a disc brake for use in a vehicle such as an automobile, and, more particularly, to a disc brake having a wear sensor or sensing member for providing a warning when the lining of a friction pad of the disc brake has become worn.
2. Prior Art
A disc brake typically comprises a pair of friction pads which are respectively positioned on the opposite sides of a disc fixedly mounted on a wheel axle. The friction pads are adapted to be forcedly pressed onto the disc to generate a braking force. A typical friction pad comprises a backing plate and a lining adhered to the backing plate.
Since the lining becomes worn as the brake is actuated, the friction pad must be replaced when the lining has been worn to a certain extent. A friction pad has been provided with a wear sensing member or sensor for indicating when the lining has been worn to its limit and that it is time for the friction pad to be replaced.
FIG. 1 is a plan view showing one example of a disc brake comprising a pair of friction pads each provided with a wear sensor as mentioned above.
Reference numeral 1 designates a rotating disc mounted on a wheel axle (not shown) to rotate therewith. On the opposite sides of the disc 1 are positioned inner and outer friction pads 2a and 2b, respectively. The friction pads 2a and 2b respectively comprise backing plates 3a, 3b and linings 4a, 4b adhered to the backing plates 3a, 3b, respectively. It is usual practice to use the same type of friction pad for both the inner and outer friction pads. Shown at 5a and 5b are wear sensors respectively mounted on the inner and outer friction pads 2a and 2b. The wear sensors 5a and 5b are fixedly secured to the rear surfaces of backing plates 3a, 3b of the respective friction pads 2a, 2b at respective one ends or base portions 6a, 6b thereof by means of rivets and the like. Respective sensing ends 7a, 7b of the sensor 5a, 5b extend over the sides of the backing plates 3a, 3b and protrude beyond the front surfaces of the backing plates by a predetermined length. In the disc brake provided with the arrangement described above, when, for example, the lining 4a has been worn to a predetermined width, the sensing end 7a of the sensor 5a contacts and is drawn by the disc 1, so that the sensor 5a vibrates and generates a noise, thereby providing a warning. When the lining 4b has been worn to the predetermined width, the sensor 5b provides a warning.
However, it should be noted that the linings 4a, 4b are never equally worn in all places over the surface contacting the disc 1. Assuming that the disc 1 rotates in the direction designated by arrow A in FIG. 1 (referred to as a regular rotating direction hereinafter) when the car advances, the lining 4a of the inner pad 2a is worn more at the entrance side (left side as viewed in FIG. 1) than at the exit side (right side as viewed in FIG. 1) while the lining 4b of the outer pad 2b is worn more at the exit side than at the entrance side. In order to enable the sensors 5a, 5b to reliably sense the wear of the lining 4a and 4b, respectively, it is necessary to mount the sensor 5a on the entrance side of the inner pad 2a and the sensor 5b on the exit side of the outer pad 2b. This arrangement also allows the use of the same type of pad with the same type of sensor for both the inner and outer pads.
However, the above-mentioned conventional disc brake suffers from the following problems.
In general, the level and nature of the noise generated by a sensor differs according to the amount of deflection of the sensor. If the amount of deflection is too small or too large, the sensor may not generate a sufficiently loud noise. In the above-mentioned conventional disc brake, the deflection of the sensor 5a for the inner pad 2a is restricted by the side of the backing plate 3a even if the sensor 5a is drawn a great amount by the disc 1 rotating in the regular rotating direction A, while the deflection of the sensor 5b for the outer pad 2b is not restricted by the backing plate 3b. If the sensors 5a, 5b are designed such that the sensor 5a, whose deflection is restricted by the side of the backing plate 3a, the sensor 5a will generate the loudest noise when it is deflected by such a restricted amount, the sensor 5b for the outer pad 2b may not operate appropriately as a wear sensor because the sensor 5b may become deflected beyond the above-mentioned amount of deflection whereby a smaller noise will be generated when it is drawn a great amount by the disc. Further, the sensor 5b of the outer pad 2b may be permanently deformed when it is drawn a great amount because of the absence of any member which acts to restrict excessive defection of the sensor. Once a sensor is permanently deformed, it cannot generate a suitable level of noise.
In order to restrict excessive deflection of the sensor 5b, the sensor 5b may be mounted on the entrance side of the outer pad 2b. In this case, however, a reliable sensing of wear by the sensor 5b cannot be expected because there is only a small amount of wear on the entrance side of the lining 4b of the outer pad 2b as mentioned above. Further, it is impossible to use the same type of pad for both the inner and outer pads, resulting in a raise in production costs of the disc brake.